"When officers arrived there were still shots being fired," said Federal Way police spokeswoman Cathy Schrock.

Investigators found two wounded men on the ground in a car park. One of the men reached for a gun as police moved in to assist the two, she said. At that point, officers opened fire. The suspect died but police said it wasn't immediately clear if it was from their gunfire.

The other man on the ground and a third man in the car park were found dead. In a search of the complex, police found a fourth man dead in one apartment and a woman dead in another unit. Police were trying to determine if the woman was hit by a stray bullet.

A total of eight officers fired their weapons. All have been placed on administrative leave, which is standard policy, as the investigation continues.

"We still don't have any idea what started this disturbance," Ms Schrock said.

After police flooded the area and carried out searches, authorities said they were confident there were no more casualties from the shooting. They said they did not think another shooter was on the loose or that there was an immediate threat to the public.

By dawn, a county medical examiner's office truck arrived at the scene to pick up bodies. Crime scene investigators continued working. One officer was seen carrying books and a gun to what appeared to be an evidence van.

There were no reports of any officers being injured. The names of the five people killed were not immediately available.